Posterior pituitary function in health and disease

[Consensus recommendations on the diagnosis and treatment of hyponatremia from the Austrian Society for Nephrology 2024]

Hyponatremia is a disorder of water homeostasis. Water balance is maintained by the collaboration of renal function and cerebral structures, which regulate thirst mechanisms and secretion of the antidiuretic hormone. Measurement of serum-osmolality, urine osmolality and urine-sodium concentration help to diagnose the different reasons for hyponatremia. Hyponatremia induces cerebral edema and might lead to severe neurological symptoms, which need acute therapy. Also, mild forms of hyponatremia should be treated causally, or at least symptomatically. An inadequate fast increase of the serum sodium level should be avoided, because it raises the risk of cerebral osmotic demyelination. Basic pathophysiological knowledge is necessary to identify the different reasons for hyponatremia which need different therapeutic procedures.

The laboratory investigation of diabetes insipidus: A review

Diabetes insipidus (DI) is a group of disorders that lead to inappropriate production of large volumes of dilute urine. The three main forms are central DI (CDI), nephrogenic DI (NDI) and primary polydipsia (PP). Differentiating CDI/NDI from PP is important as patients with true DI are at risk of severe dehydration without treatment. Biochemical testing is key in the diagnosis of DI. The indirect water deprivation test (WDT) is commonly used in the investigation of DI but has drawbacks including being cumbersome and sometimes producing equivocal results. Direct measurement of AVP has theoretical advantages but has generally only been used in specialist centres. Disadvantages include the requirement to measure AVP under hypertonic stimulation and pre-analytical/analytical challenges. Copeptin (CT-proAVP) is a proxy marker for AVP that is more stable, easier to measure and has been studied more widely in recent years. Historically, the evidence supporting the diagnostic performance of these tests has been relatively poor, being based on a few small, usually single-centre studies. However more recent, well-designed prospective studies are improving the evidence base for investigation of DI. These studies have focused on the utility of copeptin measurements during stimulation tests. There is evidence that measurement of copeptin under stimulation offers improved diagnostic performance compared to the WDT. There is currently a lack of systematic, evidence-based guidelines on the diagnosis of DI, but as the quality of the evidence defining the diagnostic performance of tests for DI continues to improve, a clearer consensus on the optimal approach should become achievable.

Consensus document on the management of hyponatraemia of the Acqua Group of the Spanish Society of Endocrinology and Nutrition

INTRODUCTION

Hyponatremia is the most prevalent electrolyte disorder in the outpatient and inpatient settings. Despite this frequency, hyponatremia, including severe hyponatremia, is frequently underestimated and inadequately treated, thus highlighting the need to produce consensus documents and clinical practice guidelines geared towards improving the diagnostic and therapeutic approach to it in a structured fashion.

MATERIAL AND METHODS

Members of the Acqua Group of the Spanish Society of Endocrinology and Nutrition (SEEN) met using a networking methodology over a period of 20 months (between October 2019 and August 2021) with the aim of discussing and developing an updated guideline for the management of hyponatraemia. A literature search of the available scientific evidence for each section presented in this document was performed.

RESULTS

A document with 8 sections was produced, which sets out to provide updated guidance on the most clinically relevant questions in the management of hyponatraemia. The management of severe hyponatraemia is based on the i.v. administration of a 3% hypertonic solution. For the management of chronic euvolemic hyponatraemia, algorithms for the initiation of treatment with the two pharmacological therapeutic options currently available in Spain are presented: urea and tolvaptan.

CONCLUSIONS

This document sets out to simplify the approach to and the treatment of hyponatraemia, making it easier to learn and thus improve the clinical approach to hyponatremia.

Cellular interactions in the pituitary stem cell niche

Stem cells in the anterior pituitary gland can give rise to all resident endocrine cells and are integral components for the appropriate development and subsequent maintenance of the organ. Located in discreet niches within the gland, stem cells are involved in bi-directional signalling with their surrounding neighbours, interactions which underpin pituitary gland homeostasis and response to organ challenge or physiological demand. In this review we highlight core signalling pathways that steer pituitary progenitors towards specific endocrine fate decisions throughout development. We further elaborate on those which are conserved in the stem cell niche postnatally, including WNT, YAP/TAZ and Notch signalling. Furthermore, we have collated a directory of single cell RNA sequencing studies carried out on pituitaries across multiple organisms, which have the potential to provide a vast database to study stem cell niche components in an unbiased manner. Reviewing published data, we highlight that stem cells are one of the main signalling hubs within the anterior pituitary. In future, coupling single cell sequencing approaches with genetic manipulation tools in vivo, will enable elucidation of how previously understudied signalling pathways function within the anterior pituitary stem cell niche.

Hyponatremia in the emergency department

Hyponatremia, defined as a serum sodium <135 mmol/L, is frequently encountered in patients presenting to the emergency department. Symptoms are often unspecific and include a recent history of falls, weakness and vertigo. Common causes of hyponatremia include diuretics, heart failure as well as Syndrome of Inappropriate Antidiuresis (SIAD) and correct diagnosis can be challenging. Emergency treatment of hyponatremia should be guided by presence of symptoms and focus on distinguishing between acute and chronic hyponatremia.

The Effect of the Dose of Isotonic Saline on the Correction of Serum Sodium in the Treatment of Hypovolemic Hyponatremia

BACKGROUND

Overcorrection of serum sodium (SNa) during therapy of hyponatremia can result in osmotic demyelination syndrome. Our aim was to determine the relationship between the isotonic saline solution dose (ISSD) administered and the 24-h SNa increase (24SNa) in patients with hypovolemic hyponatremia (HH).

METHODS

Retrospective study of HH patients treated with ISS in a tertiary hospital of Madrid, Spain, between 1 January-30 May 2019. The 24-h ISSD received and corresponding 24SNa were calculated. The latter was classified as 3 groups: ≥8 mmol/L, ≥6 mmol/L, or <4 mmol/L. Multivariate regression analyses were performed and ROC curves calculated to study the relationship between ISSD and 24SNa.

RESULTS

Thirty patients were included, age 72 years (60-80), 50% were women. 24SNa was ≥8 mmol/L/24 h in 33%, ≥6 mmol/L/24 h in 50%, and <4 mmol/L/24 h in 30%. Median ISSD in each group was: 32 mL/kg/24 h (29-37), 31 mL/kg/24 h (25-33), and 20 mL/kg/24 h (14-22), respectively. An ISSD ≥ 30 mL/kg/24 h had an odds ratio (OR) of 16 (95% CI: 2.5-95.1; p = 0.004) for a 24SNa ≥8 mmol/L, with a sensitivity and specificity of 80%.

CONCLUSIONS

The 24SNa depends on ISSD. An ISSD between 23-30 mL/kg/24 h seems to be safe and effective.

Submucosal enteric neurons of the cavine distal colon are sensitive to hypoosmolar stimuli

KEY POINTS

Neurons of the enteric submucous plexus are challenged by osmolar fluctuations during digestion and absorption of nutrients. Central neurons are very sensitive to changes in osmolality but knowledge on that issue related to enteric neurons is sparse. The present study focuses on investigation of osmosensitivity of submucosal neurons including potential molecular mediating mechanisms. Results show that submucosal neurons respond to hypoosmolar stimuli with increased activity which is partially mediated by the transient receptor potential vanilloid 4 channel. We provided important information on osmosensitive properties of enteric neurons. These data are fundamental to better explain the nerve-mediated control of the gastrointestinal functions during physiological and pathophysiological (diarrhoea) conditions.

ABSTRACT

Enteric neurons are located inside the gut wall, where they are confronted with changes in osmolality during (inter-) digestive periods. In particular, neurons of the submucous plexus (SMP), located between epithelial cells and blood vessels may sense and respond to osmotic shifts. The present study was conducted to investigate osmosensitivity of enteric submucosal neurons and the potential role of the transient receptor potential vanilloid 4 channel (TRPV4) as a mediator of enteric neuronal osmosensitivity. Therefore, freshly dissected submucosal preparations from guinea pig colon were investigated for osmosensitivity using voltage-sensitive dye and Ca²⁺ imaging. Acute hypoosmolar stimuli (final osmolality reached at ganglia of 94, 144 and 194 mOsm kg^-1 ) were applied to single ganglia using a local perfusion system. Expression of TRPV4 in the SMP was quantified using qRT-PCR, and GSK1016790A and HC-067047 were used to activate or block the receptor, respectively, revealing its relevance in enteric osmosensitivity. On average, 11.0 [7.0/17.0] % of submucosal neurons per ganglion responded to the hypoosmolar stimulus. The Ca²⁺ imaging experiments showed that glia responded to the hypoosmolar stimulus, but with a delay in comparison with neurons. mRNA expression of TRPV4 could be shown in the SMP and blockade of the receptor by HC-067047 significantly decreased the number of responding neurons (0.0 [0.0/6.3] %) while the TRPV4 agonist GSK1016790A caused action potential discharge in a subpopulation of osmosensitive enteric neurons. The results of the present study provide insight into the osmosensitivity of submucosal enteric neurons and strongly indicate the involvement of TRPV4 as an osmotransducer.

Metabolic Effects of Prostatectomy

Transurethral resection syndrome (TURS), complicating transurethral resection of the prostate (TURP) has been ascribed to hyponatraemia but reports have indicated that hyperammonaemia following metabolism of glycine can be the main cause.

Prospective data has been collected on 96 prostatectomy patients (82 TURP and 14 retropubic). The retropubic group showed no significant postoperative change in the serum sodium or plasma ammonia. Of the TURP group, no TURS occurred although hyponatraemia was noted in 32 patients. The weight of prostate resected, the volume of glycine used, the time taken and the plasma ammonia levels were not significantly different in the normonatraemic or hyponatraemic groups.

In severely hyponatraemic patients (13 out of 32 with a 10mmol/l, or greater, decrease in serum sodium) there was a significant rise (P≤0.05) in plasma ammonia, 1 or 4 h post TURP, which had decreased by 24 h.

There was a highly significant increase in serum glycine level in the hyponatraemic compared with the normonatraemic group (P≤0.001).

There was no correlation between serum glycine and plasma ammonia levels in the normonatraemic or hyponatraemic group.

There were nine patients with post TURP plasma ammonia levels ≥ 100 μmol/l (mean 254) who experienced no mental confusion: six of these patients were hyponatraemic. The weight of prostrate resected (mean 26 g), volume of glycine used (mean 181) and operation time (mean 39 min) were all relatively low.

Subsequently, TURS has occurred in a patient, with severe hyponatraemia and hyperglycinaemia but no hyperammonaemia. This study shows that hyperammonaemia does not always correlate with hyponatraemia or hyperglycinaemia, and high plasma ammonia levels can occur in the absence of TURS.

Dehydration: physiology, assessment, and performance effects

This article provides a comprehensive review of dehydration assessment and presents a unique evaluation of the dehydration and performance literature. The importance of osmolality and volume are emphasized when discussing the physiology, assessment, and performance effects of dehydration. The underappreciated physiologic distinction between a loss of hypo-osmotic body water (intracellular dehydration) and an iso-osmotic loss of body water (extracellular dehydration) is presented and argued as the single most essential aspect of dehydration assessment. The importance of diagnostic and biological variation analyses to dehydration assessment methods is reviewed and their use in gauging the true potential of any dehydration assessment method highlighted. The necessity for establishing proper baselines is discussed, as is the magnitude of dehydration required to elicit reliable and detectable osmotic or volume-mediated compensatory physiologic responses. The discussion of physiologic responses further helps inform and explain our analysis of the literature suggesting a ≥ 2% dehydration threshold for impaired endurance exercise performance mediated by volume loss. In contrast, no clear threshold or plausible mechanism(s) support the marginal, but potentially important, impairment in strength, and power observed with dehydration. Similarly, the potential for dehydration to impair cognition appears small and related primarily to distraction or discomfort. The impact of dehydration on any particular sport skill or task is therefore likely dependent upon the makeup of the task itself (e.g., endurance, strength, cognitive, and motor skill).

Clinical practice guideline on diagnosis and treatment of hyponatraemia

Hyponatraemia, defined as a serum sodium concentration <135 mmol/l, is the most common disorder of body fluid and electrolyte balance encountered in clinical practice. It can lead to a wide spectrum of clinical symptoms, from subtle to severe or even life threatening, and is associated with increased mortality, morbidity and length of hospital stay in patients presenting with a range of conditions. Despite this, the management of patients remains problematic. The prevalence of hyponatraemia in widely different conditions and the fact that hyponatraemia is managed by clinicians with a broad variety of backgrounds have fostered diverse institution- and speciality-based approaches to diagnosis and treatment. To obtain a common and holistic view, the European Society of Intensive Care Medicine (ESICM), the European Society of Endocrinology (ESE) and the European Renal Association - European Dialysis and Transplant Association (ERA-EDTA), represented by European Renal Best Practice (ERBP), have developed the Clinical Practice Guideline on the diagnostic approach and treatment of hyponatraemia as a joint venture of three societies representing specialists with a natural interest in hyponatraemia. In addition to a rigorous approach to methodology and evaluation, we were keen to ensure that the document focused on patient-important outcomes and included utility for clinicians involved in everyday practice.

Clinical practice guideline on diagnosis and treatment of hyponatraemia

Hyponatraemia, defined as a serum sodium concentration <135 mmol/l, is the most common disorder of body fluid and electrolyte balance encountered in clinical practice. It can lead to a wide spectrum of clinical symptoms, from subtle to severe or even life threatening, and is associated with increased mortality, morbidity and length of hospital stay in patients presenting with a range of conditions. Despite this, the management of patients remains problematic. The prevalence of hyponatraemia in widely different conditions and the fact that hyponatraemia is managed by clinicians with a broad variety of backgrounds have fostered diverse institution- and speciality-based approaches to diagnosis and treatment. To obtain a common and holistic view, the European Society of Intensive Care Medicine (ESICM), the European Society of Endocrinology (ESE) and the European Renal Association - European Dialysis and Transplant Association (ERA-EDTA), represented by European Renal Best Practice (ERBP), have developed the Clinical Practice Guideline on the diagnostic approach and treatment of hyponatraemia as a joint venture of three societies representing specialists with a natural interest in hyponatraemia. In addition to a rigorous approach to methodology and evaluation, we were keen to ensure that the document focused on patient-important outcomes and included utility for clinicians involved in everyday practice.

Hyponatremia and congestive heart failure: a marker of increased mortality and a target for therapy

Heart failure is one of the most common chronic medical conditions in the developed world. It is characterized by neurohormonal activation of multiple systems that can lead to clinical deterioration and significant morbidity and mortality. In this regard, hyponatremia is due to inappropriate and continued vasopressin activity despite hypoosmolality and volume overload. Hyponatremia is also due to diuretic use in an attempt to manage volume overload. When hyponatremia occurs, it is a marker of heart failure severity and identifies patients with increased mortality. The recent introduction of specific vasopressin-receptor antagonists offers a targeted pharmacological approach to these pathophysiological derangements. Thus far, clinical trials with vasopressin-receptor antagonists have demonstrated an increase in free-water excretion, improvement in serum sodium, modest improvements in dyspnea but no improvement in mortality. Continued clinical trials with these agents are needed to determine their specific role in the treatment of both chronic and decompensated heart failure.

Hyponatremia in heart failure: the role of arginine vasopressin and diuretics

PURPOSE

To provide an overview of the role of arginine vasopressin (AVP) in the development of hyponatremia in patients with heart failure (HF), the role of diuretics, and the potential for vasopressin-receptor antagonists in the treatment of HF.

METHODS

A MEDLINE literature search was performed to identify articles relating to HF, diuretics, hyponatremia, AVP, and vasopressin-receptor antagonists.

DISCUSSION

HF affects more than 5 million patients in the United States and is associated with substantial cost, morbidity, and mortality. One of the complications associated with HF, as well as with its treatment, is the development of hyponatremia. Hyponatremia in patients with HF is associated with poor outcomes and can limit the use of diuretic therapy. AVP is the primary stimulus to the development of hyponatremia in these patients and therapies that target AVP action would seem a logical choice in the therapeutic regimen for HF. Drugs that antagonize the vasopressin V(2) receptor, which is primarily responsible for water resorption in the kidney, are now available and have been studied in patients with HF. These drugs have been associated with improvements in serum sodium concentration, urine output, and body weight, but have shown no long-term mortality benefit in patients with HF. In a subset of patients with baseline hyponatremia, these agents improved quality of life scores.

CONCLUSION

Vasopressin-receptor antagonists may prove useful in the treatment of HF; however, the exact role of these agents in the treatment of HF still requires further study.

Effect of naloxone on somatostatin inhibition of arginine vasopressin response to physical exercise in normal men

To establish whether somatostatin (SRIH) and/or endogenous opioids play a role in the control of arginine-vasopressin (AVP) response to physical exercise, eight healthy men underwent four bicycle-ergometer tests until exhaustion: exercise control test; exercise plus SRIH, naloxone or SRIH plus naloxone. Serum AVP levels, physiological and biochemical variables were measured during tests. Physiological and biochemical variables were similar in all tests. During control test exercise significantly increased serum AVP levels, with a peak value 4.1 times higher than baseline. The AVP response to exercise was similar in the presence of naloxone, whereas it was significantly reduced by SRIH (AVP peak was only 2.8 times higher than baseline). When SRIH and naloxone were given together, the exercise-induced AVP rise was comparable to that observed in the control test. Results indicate a somatostatinergic involvement in the regulation of the AVP response to physical exercise. Furthermore, naloxone-sensitive endogenous opioids appear to play a role in the mechanism underlying SRIH inhibitory action, but not in mediation of the AVP response to physical exercise.

The effect of exogenous melatonin on stimulated neurohypophysial hormone release in man

OBJECTIVE

Melatonin is known to have a dose-dependent effect on basal neurohypophysial hormone release in man, low physiological doses being stimulatory and high doses inhibitory. We have performed a study to determine if this is true also for stimulated release.

DESIGN

This was a double-blind randomized crossover study with subjects being given oral doses of melatonin (0.5 mg or 5.0 mg) or placebo, before infusion of hypertonic saline or exercise.

SUBJECTS

Studies were performed on a total of 24 male subjects aged 19-23 years, who were entrained to a normal light-dark cycle and who refrained from taking heavy exercise, alcohol and smoking for 24 h prior to study.

MEASUREMENTS

Plasma vasopressin, oxytocin, sodium and osmolality and packed cell volume were measured in control samples and at regular intervals after the administration of melatonin and the challenge tests. Blood pressure and urine flow, sodium potassium and osmolality were determined during hypertonic saline infusion and blood pressure and pulse rate during exercise.

RESULTS

Plasma vasopressin increased during hypertonic saline infusion and exercise, the responses being attenuated by 5.0 mg melatonin and augmented with 0.5 mg melatonin. Although exercise had no effect on oxytocin release, there was a small but statistically significant (P < 0.05) increase in plasma oxytocin after hypertonic saline administration, which was inhibited by 5.0 mg and augmented by 0.5 mg melatonin.

CONCLUSIONS

Melatonin modulates the neurohypophysial response to different stimuli, low doses enhancing the response. This effect could contribute to the night-time increase in circulating concentrations of the hormones.

Effect of residual endogenous insulin secretion on the abnormal oxytocin response to hypoglycaemia in insulin-dependent diabetics

OBJECTIVES

Arginine-vasopressin (AVP) and oxytocin (OT) secretions are abnormally stimulated by hypoglycaemia in patients with IDDM. Since previous studies showed that AVP secretion is influenced by the persistence of residual endogenous insulin secretion, we wondered whether this factor also regulates OT secretion.

DESIGN

Case-control study: the OT response to insulin-induced hypoglycaemia was measured in normal and diabetic patients with or without residual endogenous insulin secretion.

SUBJECTS

Ten normal male subjects, 10 C-peptide positive (CpP) and 11 C-peptide negative (CpN) male diabetic patients.

PRELIMINARY STUDIES

plasma C-peptide levels were measured after intravenous administration of 1 mg glucagon. Insulin tolerance test (ITT): diabetics were studied after optimization of their metabolic status by 3 days of treatment with constant subcutaneous insulin infusion. CpP and CpN diabetics and normal controls were tested with an intravenous administration of 0.15 IU per kg body weight insulin. Blood samples for OT assay were taken just before the rapid injection of insulin (time 0) and at time 15, 30, 45 and 60 min.

RESULTS

The basal concentrations of OT were similar in all groups. Insulin induced a similar hypoglycaemic nadir in all groups at 30 min, even though diabetic groups showed a delayed recovery in blood glucose levels. The glycaemic pattern was similar in all diabetic patients. Hypoglycaemia-induced OT rise was significantly higher in the two diabetic groups than in the normal group. However, CpN patients showed significantly higher OT increments than CpP subjects.

CONCLUSIONS

These data indicate that a residual endogenous insulin secretion exerts a partial protective action against the hypothalamic-pituitary disorder affecting the OT secretory system in IDDM.

Central-peripheral temperature difference, blood pressure, and arginine vasopressin in preterm neonates undergoing volume expansion

AIM

To examine the effect of intravascular volume expansion for the treatment of hypovolaemia in sick preterm neonates.

METHODS

An intravenous infusion of 20 ml per kg of 4.5% albumin was given to 14 preterm neonates. The effects on systolic blood pressure, central peripheral temperature difference (c-pT), and plasma arginine vasopressin concentration (pAVP) were measured.

RESULTS

Thirteen babies showed a rise in systolic blood pressure. The six babies with the highest initial values of pAVP and c-pT showed a fall in both of these after infusion. The babies with lower initial pAVP (below 4 pmol/l) showed either a rise (two) or no change (six) after albumin infusion. There was a significant correlation between c-pT and log pAVP before (r2 = 0.61; p < 0.05) and after infusion (r2 = 0.45; p < 0.05).

CONCLUSIONS

Plasma AVP concentration is related to c-pT in unwell preterm newborns. This study suggests that clinical assessment of hypovolaemia in preterm newborns is poor and could be improved by using c-pT.

Gamma-aminobutyric acid mediation of the inhibitory effect of nitric oxide on the arginine vasopressin and oxytocin responses to insulin-induced hypoglycemia

Previous studies have demonstrated that the nitric oxide (NO) synthase inhibitor L-NAME exerts positive effects on the arginine vasopressin (AVP) and oxytocin (OT) responses to insulin-induced hypoglycemia, suggesting inhibitory actions of NO. The present study was designed to determine whether a gamma-aminobutyric acid (GABA)ergic pathway is involved in regulation of NO action. AVP and OT secretory patterns during insulin (0.15 IU/kg, i.v.)-tolerance tests (ITT) were examined in seven normal male subjects with (experimental tests) and without (control test) concomitant treatment with L-NAME (40 micrograms/kg injected plus 50 micrograms/kg infused, i.v.), the GABAergic agent sodium valproate (600 mg in three divided doses orally) or the combination of L-NAME and sodium valproate. Insulin-induced hypoglycemia increased by 2-fold (peak vs. baseline) plasma AVP and OT levels. In the presence of L-NAME, plasma AVP and OT levels rose 3-fold in response to hypoglycemia and were significantly higher than those in the control test. Administration of sodium valproate alone changed neither AVP nor OT secretory patterns during ITT. In contrast, sodium valproate abolished the facilitating effect of L-NAME on both AVP and OT responses to hypoglycemia. In the ITT plus L-NAME plus sodium valproate test, plasma AVP and OT levels were not significantly different at any time point from those observed during the control ITT. These data indicate a GABAergic mediation of the inhibitory modulation by NO of the AVP and OT responses to insulin-induced hypoglycemia.

Vasopressin stimulates Ca2+ spiking activity in A7r5 vascular smooth muscle cells via activation of phospholipase A2

[Arg8]-vasopressin (AVP) is both a potent vasoconstrictor and a mitogen for vascular smooth muscle cells. AVP binds to a single class of receptors (V1a) in the A7r5 rat aortic smooth muscle cell line (Kd approximately 2 nmol/L). Stimulation of these cells with AVP results in an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) by releasing intracellular Ca2+ stores and increasing Ca2+ influx; the EC50 for these effects is approximately 5 nmol/L. AVP has recently been reported to stimulate arachidonic acid release in primary cultures of rat aortic smooth muscle over a much lower concentration range (EC50 approximately 0.05 nmol/L). The present study examined the effects of varying concentrations of AVP on spontaneous Ca2+ spiking activity in fura 2-loaded A7r5 cells. Frequency of CA2+ spiking increased with increasing [AVP] in the range of 10 to 500 pmol/L. Higher concentrations of AVP inhibited spiking but elicited the characteristic [Ca2+]i changes ascribed to the release of Ca2+ stores and increased Ca2+ entry. The effects of both low and high concentrations of AVP were inhibited by [1-(beta-mercapto-beta,beta,-pentamethylenepropionic acid),2-0-methyltyrosine]arginine vasopressin, a selective V1a vasopressin antagonist. Nimodipine (50 nmol/L), a blocker of L-type voltage-sensitive Ca2+ channels, abolished the Ca(2+)-spiking activity without inhibiting a maximal [Ca2+]i response to AVP (1 mumol/L). AVP-stimulated Ca2+ spiking, but not release of intracellular Ca2+ stores, was also abolished by ONO-RS-082 (1 mumol/L), an inhibitor of phospholipase A2. These results suggest that occupation of a small fraction of V1a vasopressin receptors by AVP results in stimulation of phospholipase A2 and leads to increased Ca(2+)-spiking activity. This effect may be important for fine tuning of vascular tone, whereas maximal stimulation by AVP (full receptor occupancy) may be required for more vigorous or sustained vasoconstriction or mitogenesis.

Different effects of the serotonergic agonists buspirone and sumatriptan on the posterior pituitary hormonal responses to hypoglycemia in humans

The responses of serum oxytocin (OT) and vasopressin (AVP) to the serotonergic HT1A agonist buspirone (15 mg p.o.) or the HTD1 agonist sumatriptan (6 mg injected subcutaneously) were evaluated in 7 normal men either in basal conditions or during an insulin (0.15 iu/kg as an i.v. bolus) tolerance test (ITT). Neither buspirone nor sumatriptan administration modified the basal secretion of AVP and OT. Stimulation of 5HT-1D receptors with sumatriptan was unable to change neither AVP nor OT response to insulin-induced hypoglycemia. On the other hand, the pretreatment with the 5HT1A agonist buspirone significantly enhanced the OT response during hypoglycemia, without modifying the AVP rise. The results of this study suggest that serotonergic 5HT1A receptors may interact with hypoglycemia in the stimulation of OT, but not AVP secretion.

Sodium and water homeostasis

Disorders of sodium and water homeostasis are common occurrences in pediatric practice. They reflect distinct problems in the regulation of total body sodium balance and water distribution, respectively. Each of these groups of disorders has separate afferent and efferent mechanisms that are activated during disease states. Optimal therapy of children with fluid and electrolyte problems requires accurate delineation of the ECF volume and water distribution disturbance and the design of therapeutic regimens that account for each component of the clinical condition.

Oxytocin response to challenging stimuli in elderly men

The present study was carried out in order to establish possible alterations in oxytocin (OT) secretion with aging. Therefore, we evaluated the OT responses to insulin (0.15 U/kg)-induced hypoglycemia or to the administration of angiotensin II (i.v. infusion for 60 min of successively increasing doses of 4, 8 and 16 ng/kg min; each dose for 20 min) or apomorphine (60 micrograms/kg s.c.) in male subjects aged 22-80 yr and divided into 3 groups by age (group I (n = 9): 22-38 yr; group II (n = 9): 41-60 yr; group III (n = 9): 63-80 yr). Basal OT concentrations were similar in all groups. The OT response during the insulin tolerance test and the administration of ANG II had similar patterns and magnitudes in all groups. The OT response to apomorphine was similar in the two younger groups, with plasma OT levels increased 118% vs. baseline. In contrast, apomorphine was unable to induce a significant OT rise in the oldest group. During apomorphine test plasma OT concentrations were significantly lower in group III than in groups I and II. For the first time in elderly human subjects, these data show normal responsiveness of the OT secretory system to releasing stimuli such as hypoglycemia and ANG II. These findings indicate that in aged men production of OT and capability of responding to challenging stimuli is unchanged. On the other hand, the reduced OT responsiveness to apomorphine in group III might be an expression of the general dopaminergic dysfunction affecting the aging brain.

A patient with monosomy 7 and polyuria

Diabetes insipidus (DI) is a rare complication of leukaemia. An association between monosomy 7 and DI in leukaemias has been proposed. We present a case of Ph1-positive CML who developed polyuria at the time of lymphoid blast transformation associated with loss of chromosome 7. Biochemical results were not diagnostic of DI and a therapeutic trial of DDAVP was unsuccessful. Post-mortem showed a peripituitary and renal leukaemic infiltrate and although DI is a possibility, the cause of his polyuria remains unresolved.

Effects of intravenous infusion of substance P on arginine vasopressin and oxytocin secretion in normal men

In order to establish possible stimulatory effects of increasing plasma concentrations of substance P (SP) on the arginine vasopressin (AVP) and/or oxytocin (OT) secretion, successively increasing doses of SP(0.5, 1 and 1.5 pmol/kg-1/min-1; each dose for 20 min) were infused in 7 normal men. Plasma AVP and OT levels were measured before infusion and every 20 min, just before increasing the infusion dose of SP. During tests, SP infusion did not produce untoward side effects or changes in blood osmolality and/or pressure. Plasma OT levels did not change during SP infusion. Plasma AVP concentrations were not modified by the infusion of the lowest dose of SP, whereas they were significantly increased in a dose response fashion when higher amounts of SP were given. These findings demonstrate for the first time in humans that the systemic administration of SP exerts stimulatory effects on AVP, but not on OT secretion.

Cell volume regulation: a review of cerebral adaptive mechanisms and implications for clinical treatment of osmolal disturbances: II

Cerebral cell volume regulatory mechanisms are activated by sustained disturbances in plasma osmolality. Acute hypernatremia causes a predictable shrinkage of brain cells due to the sudden imposition of a plasma-to-cell osmolal gradient. However, during chronic hypernatremia cerebral cell volume is maintained close to the normal range as a result of the accumulation of electrolytes and organic osmolytes including myo-inositol, taurine, glutamine, glycerophosphorylcholine, and betaine. The increased cytosolic level of these molecules is generally accomplished via increased activity of sodium (Na+)-dependent cotransport systems. The slow dissipation of these additional osmotically active solutes from the cell during treatment of hypernatremia necessitates gradual correction of this electrolyte abnormality. Acute hyponatremia leads to cerebral cell swelling and severe neurological dysfunction. However, prolonged hyponatremia is associated with significant reductions in brain cell electrolyte and organic osmolyte content so that cerebral cell volume is restored to normal. While acute hyponatremia can be treated with the administration of moderate doses of hypertonic saline in order to control seizure activity, chronic hyponatremia should be corrected slowly in order to prevent subsequent neurological deterioration. If the rate of correction exceeds 0.5 mmol/l per hour, or if the total increment in serum [Na+] exceeds 25 mmol/l in the first 48 h of therapy, then there is an increased risk of the development of cerebral demyelinating lesions. Chronic hyperglycemia activates the brain cell volume regulatory adaptations in the same manner as hypernatremia. Therefore, during the treatment of diabetic ketoacidosis, it is imperative to restore normoglycemia gradually in order to prevent the occurrence of cerebral edema.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of plasma vasopressin in spontaneous migraine

Vasopressin is a vasoactive hormone secreted from the posterior pituitary. At low concentration its role is in regulating renal water excretion, but at higher concentrations it has a number of extrarenal actions, including effects on blood flow. To investigate the role of vasopressin in spontaneous migraine, paired samples were collected from 14 subjects (a) during an acute attack of spontaneous migraine, and (b) when symptom-free for at least seven days. During an attack, vasopressin was consistently raised (median (range) 3.5 (1.2-9.6) pg/ml v 0.5 (0.5-1.1) pg/ml, p less than 0.001). The highest vasopressin concentration occurred in the only patient who vomited. The results suggest vasopressin rises during an attack of spontaneous migraine, and this may, in part, be related to emesis. In the majority, vasopressin levels only rose sufficiently to have some renal antidiuretic effect, although in some these levels could have been sufficient to cause alteration in peripheral blood flow. Release of vasopressin may be responsible for the facial pallor and antidiuresis observed in migraine.

Effect of estrogen or insulin-induced hypoglycemia on plasma oxytocin levels in bulimia and anorexia nervosa

Plasma oxytocin (OT) levels were measured before and after stimulation with estrogens (1 mg ethynylestradiol orally) or with insulin (0.15 IU/kg)-induced hypoglycemia in seven underweight women with anorexia nervosa, eight normal weight bulimic women, and nine normal controls. Anorectic patients were amenorrhoic; they were tested at their first hospitalization (first tests) and again 8 to 9 weeks later (second tests) when they were eating normally, but were still at a low weight. In addition, anorectic women were tested 16 to 17 weeks after the first test (third tests), when their weight was restored to normal. Normal and bulimic women were tested on the fourth days of normal menstrual cycles. Insulin induced similar hypoglycemic responses in all groups. At each time point of the estrogen tests, plasma estrogen levels were similar in bulimic and normal women, whereas they were significantly lower in anorectic subjects. There were no differences in the basal levels of OT among groups. Both insulin-induced hypoglycemia and estrogen treatment produced striking OT increments in bulimic and control women, without significant differences between groups. During the first tests, no significant increase in plasma OT levels was observed in underweight anorectic women in response to both releasing stimuli. After partial weight recovery, the anorectic women showed a slight, but significant, increase in the OT responses to both insulin-induced hypoglycemia and estrogen administration. Both hypoglycemia- and estrogen-induced OT increases observed during the second tests were significantly lower in underweight anorectic patients than in normal controls. Anorectic subjects regained normal OT responsiveness to both stimuli after complete weight recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxytocin does not modify the prolactin response to metoclopramide in normal women

The present study was undertaken in order to establish whether oxytocin (OT) affects the dopaminergic control of PRL secretion in normal women during follicular, periovulatory and luteal phase of their menstrual cycle. For this purpose, 22 normal women were tested with a lower (1 mg) or higher (10 mg) dose of the dopaminergic antagonist metoclopramide (MCP) with or without the concurrent treatment with OT (2 IU injected plus 0.033 IU/min infused for 2 h). Since OT was found unable to modify the effect of either 1 or 10 mg MCP, in additional experiments the same doses of MCP and OT were administered after dopamine (0.04 micrograms/kg/min for 2 h) infusion. Also in these experimental conditions OT failed to modify the PRL response to MCP. These data argue against a role of OT in modulation of the dopaminergic control of PRL secretion in normal women.

Endogenous opioid mediation of somatostatin inhibition of arginine vasopressin release evoked by insulin-induced hypoglycemia in man

In order to establish whether endogenous opioids play a role in the control of arginine vasopressin (AVP) response to insulin-induced hypoglycemia by interacting with somatostatin (SRIH), seven normal men were submitted to an insulin (0.15 U/kg) tolerance test (ITT) in the presence or absence of naloxone (10 mg in an i.v. bolus), SRIH (4.1 micrograms/min x 90 min) or the combination of the two substances. Plasma AVP concentrations rose significantly during ITT. The AVP response remained unchanged in the presence of naloxone, whereas it was significantly reduced by the treatment with SRIH. When both SRIH and naloxone were given, the hypoglycemia induced AVP rise was similar to that observed in the control test. These results indicate the involvement of naloxone sensitive endogenous opioids in the mechanism underlying SRIH inhibitory action, but not in the mediation of the AVP response to hypoglycemia.

Increase by naloxone of arginine vasopressin and oxytocin responses to insulin-induced hypoglycemia in obese men

The present study was carried out to establish whether the low arginine vasopressin (AVP) and oxytocin (OT) responses to insulin-induced hypoglycemia observed in obese men was due to alteration of the opioid control of posterior pituitary function. For this purpose, the AVP and OT releasing effect of insulin (0.15 IU/kg bw)--induced hypoglycemia was tested in eight normal weight men and in 10 age-matched obese subjects, without and with the previous treatment with the specific opioid receptor antagonist naloxone (3 mg in an iv bolus). In a control study, naloxone was given alone to the same subjects. Obese men showed similar basal glucose, AVP and OT levels, which remained unmodified after treatment with naloxone alone. Insulin induced a similar decrement of blood glucose levels in all subjects, with a nadir at 30 min. Plasma levels of AVP and OT rose strikingly in normal and obese subjects with mean peak responses at 30 min for AVP and at 45 min for OT. However, both AVP and OT responses were significantly lower in obese than in control subjects. Pretreatment with naloxone did not modify the AVP and OT responses to hypoglycemia in normal weight subjects, whereas it significantly enhanced both hormonal responses in obese subjects. In the presence of naloxone normal controls and obese subjects showed similar responses of both AVP and OT to hypoglycemia. These data indicate that an abnormal activity of endogenous opioids might account for the hypothalamic posterior pituitary dysfunction, which is responsible for the low AVP and OT responses to insulin-induced hypoglycemia in obesity.

Effect of obesity and weight loss on arginine vasopressin response to metoclopramide and nicotine from cigarette smoking

We have previously reported an impaired arginine vasopressin (AVP) response to insulin-induced hypoglycemia in obese men, suggesting a hypothalamic-posterior pituitary disorder in obesity. In the present study, we examined the AVP response to other releasing stimuli with a central site of action. The AVP response of 10 obese men to metoclopramide (MCP) or nicotine inhaled with cigarette smoking was compared with that obtained in eight sex- and age-matched controls. The AVP increase during nicotine and MCP tests were significantly lower in the obese patients than in the normal controls. Obese men were restudied after substantial weight loss. The AVP response to nicotine and MCP administration was significantly higher than before slimming and did not differ from that observed in the normal weight subjects. These results demonstrate obesity-related alterations in the AVP responsiveness to nicotine inhaled with cigarette smoking and MCP, supporting the hypothesis for a hypothalamic-posterior pituitary disorder in obesity.

Muscarinic cholinergic, but not serotoninergic mediation of arginine vasopressin response to metoclopramide in man

The possibility that metoclopramide (MCP) stimulates arginine vasopressin (AVP) secretion in man through a serotoninergic and/or a cholinergic muscarinic pathway was studied. Twenty normal male subjects were tested with MCP (10 mg in an i.v. bolus) alone or in the presence of the 5HT1 serotoninergic antagonist metergoline (10 mg/day p.o. in five divided doses for 4 days), the 5HT2 receptor blocker ketanserin (10 mg i.v. 5 min before MCP) (n = 10), the M1 and M2 muscarinic antagonist atropine (1.2 mg i.v. just before MCP administration) or the M1 muscarinic receptor blocker pirenzepine (40 mg i.v. 10 min before MCP) (n = 10). AVP doubled in response to MCP. the MCP-induced AVP rise did not change after metergoline, ketanserin or pirenzepine administration, whereas it was abolished by atropine. Additional experiments were performed in order to evaluate the effect of 1.2 mg atropine, given alone, on circulating AVP levels and whether the effect of atropine on the AVP response to MCP depends on the amount of the muscarinic antagonist (dose-response study). For these purposes, atropine was given alone to the same subjects previously tested with MCP plus atropine; furthermore, eight additional male subjects were tested with MCP plus atropine given in doses ranging from 0.8 to 1.4 mg. The results of these additional studies failed to show an effect of atropine alone on AVP secretion and demonstrated a dose-related inhibition of MCP-induced AVP rise by increasing atropine administration from 0.8 mg to 1.2 mg.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of vasopressin secretion

With the development of sensitive and specific radio-immunoassays to measure the low circulating concentrations of vasopressin there has been a quantum leap in our understanding of the physiological processes involved in the regulation of its secretion. The results of Verney's pioneering studies in dogs led to the concept of 'osmoreceptors'. It is now appreciated that osmoregulation of vasopressin release is of principal importance in the maintenance of water balance. Functional characteristics of the osmoregulatory system have been defined clearly by independent laboratories, and more recently the physiological influences that can subtly alter this very finely controlled system have been described. Non-osmotic factors that release vasopressin have been recognized for many years. Secretion of vasopressin in response to haemodynamic influences has been characterized, and significant hypotension and/or hypovolaemia are potent stimuli to hormone release. Other non-osmotic factors--nausea/emesis, hypoglycaemia--may play important roles in disturbances of water balance. Vasopressin should not, however, be regarded as a stress hormone, since recent careful studies in a variety of species indicate that secretion is not enhanced following a series of different noxious stimuli.

Short-term hemodynamic effects of vasopressin V1-receptor inhibition in chronic right-sided congestive heart failure

Arginine vasopressin is elevated in congestive heart failure. To determine the effect of arginine vasopressin upon systemic hemodynamics and regional blood flows, we administered the specific inhibitor of the vascular action of vasopressin [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),2-(O-methyl)-tyrosine]-arginine vasopressin [d(CH2)5Tyr(Me)AVP] to 15 dogs with chronic right-heart failure produced by tricuspid avulsion and progressive pulmonary artery constriction. The animals exhibited increased plasma arginine vasopressin and norepinephrine levels. Vasopressin inhibition increased cardiac output and left ventricular dP/dt and dP/dt/P, and it decreased total peripheral vascular resistance, whereas mean aortic pressure did not change significantly. Simultaneously, blood flow increased to skeletal muscle, kidneys, skin, and right and left ventricular myocardium. Plasma catecholamines also increased. Pretreatment with propranolol and prazosin abolished the increases in cardiac output and left ventricular function produced by vasopressin inhibition. Pretreatment also led to a decrease in mean aortic pressure after vasopressor inhibition. In contrast, administration of d(CH)2)5Tyr(Me)AVP to 11 sham-operated animals or administration of normal saline to nine sham-operated and eight heart-failure dogs was without effect either in the absence or in the presence of adrenergic receptor blockade. Thus, arginine vasopressin participates in the control of the circulation in right-sided congestive heart failure, with both a direct constrictor action on blood vessels and an indirect action by inhibition of the sympathetic nervous system.

Osmoregulation of vasopressin secretion and thirst in cyclical oedema

Osmoregulation of vasopressin release and thirst was studied in the mid-follicular and mid-luteal phases of the menstrual cycle of five patients with cyclical oedema defined by peripheral oedema and weight gain (greater than 3.0 kg) manifest in two consecutive luteal phases. Results are compared to those already obtained in eight healthy women. In the patients, basal plasma osmolality in the mid-luteal phase was significantly lower than in the mid-follicular periods (patients, 283 +/- 1, 287 +/- 1 mOsmol/kg, respectively, mean +/- SEM, P less than 0.05; controls, 282 +/- 1, 286 +/- 1 mOsmol/kg, respectively, P less than 0.05). Plasma osmolality (pOsm) and plasma arginine vasopressin (pAVP) were measured during hypertonic (850 mmol/l) saline infusion in both phases of the cycle; linear regression analyses of these data gave the following mean regression equations, (i) mid-follicular, pAVP = 0.55 (pOsm - 285), r = 0.94 and (ii) mid-luteal, pAVP = 0.42 (pOsm - 281), r = 0.93. The abscissal intercept was significantly different (P less than 0.025). Osmotic threshold for severe thirst onset was lower in the mid-luteal phase compared to the mid-follicular value (296 +/- 1, 299 +/- 1 mOsmol/kg, respectively, P less than 0.01). Basal data and results of thirst onset and theoretical threshold for vasopressin release in response to osmotic stimulation obtained in the patients were similar to healthy control women. We conclude that osmoregulation in cyclical oedema is normal.

Oxytocin response to insulin-induced hypoglycemia in obese subjects before and after weight loss

The response of plasma oxytocin to an iv bolus injection of crystalline insulin (0.15 U/kg) was evaluated in 14 normal weight [mean body mass index (BMI) = 23] and in 9 obese (mean BMI = 42) men. Similar blood glucose decrements after insulin injection were observed in the two groups. Obese and normal weight subjects presented similar basal oxytocin levels. In both groups, oxytocin rose significantly during the insulin tolerance test (ITT); however, the peak oxytocin response in the obese men was significantly lower than in the normal weight subjects. Obese men were restudied after substantial weight loss. Basal oxytocin levels and glucose response to insulin did not change after weight reduction. The oxytocin response to the ITT was significantly higher than before slimming and did not differ from that observed in the normal weight subjects. A significant negative correlation between BMI values and oxytocin peak levels during ITT was observed in the lean controls and obese subjects (r = 0.516, p less than 0.02). These results demonstrate that in obese subjects the oxytocin secretory response during an insulin tolerance test is reduced, suggesting the existence of a hypothalamic-pituitary disorder in obesity.

Differential release of vasopressin and oxytocin in response to abdominal vagal afferent stimulation or apomorphine in the ferret

The aim of this study was to investigate whether direct afferent stimulation of the abdominal vagus could promote release of the neurohypophyseal hormones. The nucleus of the solitary tract is the major recipient of vagal afferent information, and this region of the brainstem may also be activated by stimulation of the area postrema. For this reason apomorphine, a D2 dopaminergic agonist which acts on the area postrema, and can evoke vasopressin secretion in man, was also investigated for its effect on vasopressin and oxytocin release. Our results show that vasopressin, but not oxytocin is released in vast amounts in response to electrical afferent stimulation of the abdominal vagus. Administration of apomorphine also evoked a massive vasopressin release with less marked effects on oxytocin. The possible functional implications of these results are discussed especially in the context of nausea and vomiting.

Hypernatraemia due to a reset osmostat for vasopressin release and thirst, complicated by nephrogenic diabetes insipidus

We describe a patient with chronic hypernatraemia (plasma sodium 148-155 mmol/l) and partial nephrogenic diabetes insipidus who had received prolonged lithium treatment. Despite stopping the drug for one year the abnormalities remained. Infusion of hypertonic saline (NaCl 855 mmol/l) allowed the characterization of osmoregulation of thirst and vasopressin secretion. Linear regression analysis of plasma vasopressin and osmolality defined the function, pAVP = 0.27 (pOsm - 301), and analysis of thirst measured by a visual analogue scale and plasma osmolality, the function, thirst = 0.16 (pOsm - 302) where pAVP and pOsm represent plasma arginine vasopressin and osmolality respectively. The slopes of the regression lines which describe the sensitivity of the osmoreceptors were within the normal range, but both abscissal intercepts, which define the thresholds for vasopressin release and thirst, were markedly elevated in comparison to normal (upper limit less than 290 mOsm/kg). Other investigations of electrolytes, anterior pituitary function and high definition computed tomographic scanning of hypothalamo-pituitary region were all normal. We conclude that this patient's chronic hypernatraemia was due to resetting of the osmostats for both vasopressin release and thirst, a rarely described mechanism to account for hypernatraemia. Although it is probable that the partial nephrogenic diabetes insipidus was related to prolonged lithium therapy, the cause of the reset osmostats remains unclear.

Plasma oxytocin, arginine vasopressin and atrial natriuretic peptide responses to insulin-induced hypoglycaemia in man

The changes in blood glucose, plasma oxytocin, plasma vasopressin, plasma atrial natriuretic peptide, serum osmolality, haematocrit and blood pressure were measured in response to acute insulin-induced hypoglycaemia in six normal male subjects. After the i.v. administration of insulin (0.15 U/kg), plasma concentrations of oxytocin and vasopressin increased rapidly in all subjects and were maximal 15 min after the acute hypoglycaemic reaction (R). Haematocrit increased at the time of the hypoglycaemic reaction, but there was no change in serum osmolality. Systolic blood pressure rose and diastolic blood pressure fell, but mean arterial blood pressure remained unchanged. No changes were demonstrated in plasma concentrations of atrial natriuretic peptide. The release of oxytocin and vasopressin in response to acute hypoglycaemia in man is probably caused by stimulation of the posterior pituitary gland via hypothalamic activation, and not by stimulation of osmoreceptors or baroreceptors.

Influence of nifedipine and enalapril on osmoregulation of vasopressin

To determine whether calcium fluxes and angiotensin II influence osmoregulation of vasopressin (AVP) secretion, the effects of the calcium antagonist nifedipine and of the converting enzyme inhibitor enalapril on the AVP response to an osmotic load were compared to those of a placebo in seven normal female subjects. Plasma and urinary AVP were measured before and during a 3-h infusion of 2.5% hypertonic saline. Nifedipine (10 mg orally 2 h before and 10 mg at the start of the infusion) increased heart rate but did not change blood pressure. The changes in free water clearance and in urinary AVP induced by hypertonic saline under nifedipine were greater than in the control test, but the slope and the intercept of the regression line of plasma AVP upon plasma osmolality were not significantly different. Enalapril (10 mg 3 h before the infusion) did not change heart rate or blood pressure. Free water clearance and urinary AVP did not differ from the control test, but the slope of the regression line was less steep. These slight modifications of the response to an osmotic load suggest that calcium fluxes and angiotensin II only exert a limited influence on AVP osmoregulation in normal females.

Recumbent cranial diabetes insipidus. Studies in a patient with adipsia, hypernatremia, poikilothermia and polyphagia

A male, aged 16, with chronic hypernatremia, adipsia, polyphagia, and poikilothermia was studied regarding regulation and secretion of arginine vasopressin. During recumbency at night, low plasma arginine vasopressin levels and increased volumes of dilute urine were found; whereas plasma arginine vasopressin levels and urine osmolalities rose and urine volumes decreased during ambulation in the daytime. Neither a 25% reduction of mean arterial pressure nor hypertonic saline infusion increased plasma arginine vasopressin or urine osmolalities. Treatment with 1-desamino-D-arginine-vasopressin at 6 p.m. and a scheduled fluid intake according to actual body weight eradicated hypernatremia and hyperosmolality. These data demonstrate a complete loss of arginine vasopressin secretion to osmotic stimulation, a partial defect of arginine vasopressin secretion to non-osmotic stimulation, an abolished response to stimulation of high-pressure-baroreceptors, but an intact responsiveness to stimulation of low-pressure-baroreceptors.